The present invention relates to electron beam lithography technology to be applied to LSI manufacturing processes, and to a lithography system and method aiming at manufacturing fine and highly integrated devices.
Integrated devices such as semiconductor memory devices are becoming finer and highly integrated more and more. Innovations on manufacturing technology, particularly lithography technology, are immense. The minimum work dimension of recent highly integrated devices is in the order of sub-micron. Lithography technology which can perform such a fine work is electron beam lithography technology. This electron beam lithography technology has a feature that it can process a finer pattern than other lithography technology such as optical type lithography technology. A typical example of electron beam lithography technology is disclosed in Japanese Patent Laid-Open Publication JP-A-59-169131. As shown in FIG. 1, a conventional electron beam lithography system is constructed of an electron gun 1 for generating an electron beam, two apertures 2 and 26 for shaping the beam in the form of square, lenses 3 and 5, deflectors 4, 27 and 28, a projection lens 11, and an objective lens 12. Electrons generated by the electron gun 1 are shaped by the first square aperture 2 to obtain a square shaped beam having a uniform current distribution which beam is then focussed on the second aperture 26 by the two lenses 3 and 5. The electron beam shaped by the second aperture 26 of a square shape or any desired shape is focussed onto a specimen 13 via the projection lens 11 and objective lens 12 to expose resist on the specimen.
In operation of the above-described conventional electron beam lithography system, an electron beam entered the resist is forward scattered, and the beam on the substrate surface is back scattered. Therefore, the resist area which should not be exposed is locally exposed, resulting in a so-called proximity effect. A degree of such scattering changes depending upon the material of a substrate and a pattern density. Therefore, even the patterns of the same design will have different dimensions after development, depending upon the densities of adjacent patterns and the substrate material. There is also associated with a problem that if the same pattern is repetitively drawn, the dimensions after development become different between the central areas and peripheral areas of the pattern. For repetitive patterns or patterns with various pattern densities used when manufacturing highly integrated devices, it is therefore impossible to obtain uniform dimensions as designed. In order to solve the above problems, parameters of pattern data have been conventionally changed in each lithography operation, such as changing the electron beam exposure time in accordance with a dimension or a pattern density. With this method, however, it is essential that the amount of pattern data is increased, resulting in a very long pattern preparatory time and drawing time.
Furthermore, with the above-described conventional electron beam lithography system, a great amount of transmitted electron beam energy is required for drawing a pattern having a large aperture area. As a result, the focus position of the electron optics displaces from the specimen surface, giving a so-called space charge effect. With a conventional method, if a large pattern is to be drawn, the pattern is divided into smaller patterns which are not influenced by the above-described effect, resulting in a necessity of a long time for drawing the patterns.